Article: Classification of the trilobite Pseudagnostus

Eighty-eight species assigned or assignable to Pseudagnostus sensu lato are divided into two broad divisions based on the position of the glabellar node with respect to the anterior or anterolateral glabellar furrows and anterolateral lobes. A spectaculate division, in which the node lies to the rear of the anterior furrow and to the rear of the anterolateral lobes, is divided into nine species groups which are recognized by degree of effacement of external morphology, shield shape, border morphology, glabellar morphology, pygidial spinosity, and metamerism. Three spectaculate species groups, bulgosus, communis, and cyclopyge, are referred to Pseudagnostus Jaekel, 1909, sensu stricto; one, contracta, to Pseudagnostina Palmer, 1962; and one, securiger, to Sulcatagnostus Kobayashi, 1937, these latter taxa being regarded as subgenera of Pseudagnostus. Four other spectaculate species groups, araneavelatus, bilobus, canadensis, and clavus, are classified with Neoagnostus Kobayashi, 1955, pending clarification of the taxonomic status and concepts of Euplethagnostus Lermontova, 1940, and Pseudorhaptagnostus Lermon-tova, 1940. Hyperagnostus Kobayashi, 1955 and Machairagnostus Harrington and Leanza, 1957 are synonymized with Neoagnostus. A papilionate division, in which the axial glabellar node lies between the anterolateral lobes and interrupts the course of the anterior furrow, consists of two species groups, convergens and clarki, which are assigned to Rhaptagnostus Whitehouse, 1936. The generic name Plethagnostus Clark, 1923 is suppressed.